The invention relates to a control device for operating a road-coupled hybrid vehicle equipped with at least one electronic control unit, a first drive unit (for example, with an electric motor as the drive motor) which is assigned to a first axle (for example, the front axle), and a second drive unit (for example, with an internal combustion engine as the drive motor) which is assigned to a second axle (for example, the rear axle).
The first drive unit and the second drive unit are not coupled with respect to the drive via a vehicle-internal mechanical clutch or longitudinal lock but instead merely by means of the road via the wheels. Such road-coupled hybrid vehicles are also referred as to “axle-split” hybrid vehicles. In this context, an electric motor is preferably used as the primary motor and an internal combustion engine as the secondary motor.
Various methods for operating a road-coupled hybrid vehicle are described, For example, in German Patent applications 10 2012 211 920, 10 2013 208 965 or 10 2013 219 085.
Hybrid vehicles of this type can be operated, in particular, in a first operating mode (preferably, an e-mode for purely electric driving) in which the electric motor is operated alone as a primary motor in order to control the drive, and in a second operating mode (preferably, an a-mode for automatically controlled electric and/or internal combustion engine driving) in which the internal combustion engine can also be automatically connected and disconnected as a secondary motor for controlling the drive.
German Patent applications 10 2012 211 920 and 10 2013 208 965 are concerned with a method for connecting the secondary motor.
In German Patent application 10 2013 219 085, the emphasis is on driving-performance-optimizing and consumption-optimizing drive strategies for actuating the primary and secondary motors for drive-oriented driving. In contrast, in the case of driving-dynamics oriented driving, in particular when there is a demand for traction, the emphasis is on the drive torque distribution between the axles.
The object of the invention is to improve a hybrid vehicle of the type mentioned at the outset with respect to an optimum compromise between achieving a high electric starting acceleration with a high drive torque and achieving the highest possible maximum vehicle velocity.
This and other objects are achieved according to the invention by a control device for operating a road-coupled hybrid vehicle having a first drive unit which is assigned to a first axle and having a second drive unit which is assigned to a second axle. A selector device can be operated by the driver for manually changing between a purely electric operating mode and an automatic operating mode. At least one electronic control unit controls the drive units at least partially also as a function of the operator control of the selector device, wherein the first drive unit has an electric motor and a two-speed transmission which can be shifted automatically and interacts with the electric motor, and wherein the second drive unit has an internal combustion engine and an additional transmission which interacts with the internal combustion engine.
The invention is based on a specific electromechanically controllable two-speed transmission with synchronized gear-speed changing processes, which two-speed transmission is assigned to an electric motor as a drive motor. This first (electric) drive unit composed of an electric motor as the drive motor and the above-mentioned two-speed transmission acts on a first axle of a hybrid vehicle and does not have a vehicle-internal mechanical connection to a second (internal combustion engine) drive unit on the second axle of the hybrid vehicle.
The control device according to the invention for controlling the change of gear speed in the two-speed transmission takes into account different drive modes in a hybrid vehicle, in particular in the event of a change from an automatic hybrid mode (a-mode) into a purely electric operating mode (e-mode), and vice versa.
The invention also relates to a control device for the sequence control of the change of the gear speed in the two-speed transmission, which change of gear speed is initiated with a reduction in the torque of the electric motor; this is because the device according to the invention does not provide a clutch between the electric motor and the two-speed transmission.
The inventive reduction in torque of the electric motor is preferably compensated for in the case of a change of gear speed at the first axle by the second drive unit on the second axle by road coupling, insofar as the second drive unit is not switched off or cannot be connected quickly enough.
The invention is based on the following considerations.
Combining an internal combustion engine and an e-machine (=electric motor) permits various operating modes (for example, purely electric driving, purely internal combustion engine driving or combined electric and internal combustion engine driving). For example, in the a-mode the internal combustion engine and the e-machine preferably operate together to provide strong acceleration. As a rule, in the case of acceleration, the e-machine serves for briefly feeding in high torques, since the internal combustion engine has a relatively slow time behavior.
The invention will be explained by way of example on the basis of a “split-axle” hybrid vehicle concept in which the e-machine is located as a central drive on the front axle, and the internal combustion engine is located as a central drive on the rear axle. The two drive technologies can be operated independently of one another and can also be coupled functionally to one another with respect to a wheel-torque-related torque structure by way of at least one electronic control unit, which is assigned to both drive technologies.
With respect to the technical background, reference is additionally made to a lecture by the Applicant at the 22nd Aachener Kolloquium in October 2013, in which reference is already made to a number of the concept considerations regarding the new BMW i8 vehicle (planned series production in March 2014) which preceded the invention. Furthermore, with respect to the general wheel-torque-related torque structure within the scope of the coupled drive control by way of an engine control unit (DME) in a road-coupled hybrid vehicle, reference is made by the Applicant to the earlier German Patent applications DE 10 2011 004 862 and DE 10 2011 005 962.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.